About 130 pairs of hands and a "year's worth" of weekends have helped complete a predator-proof fence perched above the cliffs of St Clair, Dunedin.

Constructing the fence about 70m above the rocks between St Clair and Tunnel Beach has had its challenges, but just over two years later, it is complete.

The Forest and Bird Dunedin branch project aims to protect a small population of fairy prions - the only mainland population of the seabird - and attract other seabirds back to the city's coast.

Forest and Bird Dunedin branch member Graeme Loh, who looks after the fairy prions, said the work started in April 2011 after a flying fox-type system was devised to get heavy material down to the site.

Workers took a break during the summer of 2011-12 and then got stuck in, with about 130 volunteers giving their time to help complete the project, which was funded by the Marjorie Barclay Trust.

Once the final cap was put in place, a team of Otago Polytechnic students abseiled down the cliffs to retrieve material that had fallen over the edge during construction.

"We had a few bins blown over the edge, trowels and I think I lost five measuring tapes."

Now, the focus was on ridding the enclosure of mice and monitoring to see if there were any rats inside.

"Instead of a million-dollar mouse project, ours will be more like a $20 mouse project."

Fairy prions were already nesting in the holes of the cliff below the fence and there were plans to build nesting boxes and dig burrows to attract other seabirds, such as sooty shearwaters and diving petrels, to the enclosure.

A sound system funded by the Speight's Fund would be used to "call" other birds in, and earth with seabird droppings in it would be scattered to appeal to their sense of smell, Mr Loh said.